Electrostatic capacity-type pressure sensor with reduced variation in reference capacitance

ABSTRACT

A capacitance-type pressure sensor capable of reducing a variation in reference capacitance. The capacitance-type pressure sensor includes insulating spacer (3b) arranged between a main capacitive electrode (4) and a reference capacitive electrode (5) to couple a base substrate (1) and a diaphragm substrate (2) to each other. The insulating spacer (3b) is patterned so as to restrain a variation in distance between the reference capacitive electrode (5) and a counter electrode (10) arranged on the diaphragm substrate (2). Such construction reduces a variation in capacitance between the reference capacitive electrode (5) and the diaphragm electrode (10), to thereby increase accuracy at which a pressure is measured.

TECHNICAL FIELD

This invention relates to a capacitance-type pressure sensor adapted tomeasure a pressure based on a variation in capacitance.

BACKGROUND ART

U.S. Pat. No. 4,774,626 (corresponding to Japanese Patent ApplicationLaid-Open Publication No. 19527/1988) discloses a capacitance-typepressure sensor which includes a base substrate provided thereon with amain capacitive electrode and a diaphragm substrate provided thereonwith a counter electrode in a manner to be opposite to the maincapacitive electrode and is so constructed that the base substrate anddiaphragm substrate are joined at an outer periphery thereof to eachother through a layer of sealing material, as well as a pressure sensormodule including such a capacitance-type pressure sensor. U.S. Pat. No.4,888,662 likewise discloses a pressure sensor module including acapacitance-type pressure sensor. As seen in each of the U.S. patents,fluid of which a pressure is to be measured is contacted with a rearsurface of the diaphragm substrate of the pressure sensor.

U.S. Pat. Nos. 4,329,732, 4,735,098, 4,680,971 and 4,425,799 eachdisclose a capacitance-type pressure sensor wherein a base substrate isprovided thereon with a reference capacitive electrode separately from amain capacitive electrode.

FIG. 19(A) schematically shows a conventional capacitance-type pressuresensor which includes a base electrode provided thereon with a maincapacitive electrode and a reference capacitive electrode. Theconventional capacitance-type pressure sensor includes a base substrate31, which is formed thereon with a main capacitive electrode 32 and areference capacitive electrode 33 in a manner to be spaced from eachother at predetermined intervals. Also, it includes a diaphragmsubstrate 34, which is formed thereon with a diaphragm electrode 35 in amanner to be opposite to the main and reference capacitive electrodes 32and 33. In the conventional capacitance-type pressure sensor thusconstructed, external application of a pressure P of fluid which is tobe measured to the diaphragm substrate 34 leads to deflection of thediaphragm substrate 34, resulting in a distance or interval between themain capacitive electrode 32 and the diaphragm electrode 35 being variedfrom D0 to D1, so that a capacitance between the main capacitiveelectrode 32 and the diaphragm electrode 35 may be varied, as shown inFIG. 19(B). Such a capacitance-type pressure sensor permits the pressureP to be measured or calculated on the basis of both a capacitance variedbetween the main capacitive electrode 32 and the diaphragm electrode 35and a reference capacitance between the reference capacitive electrode33 and the diaphragm electrode 35.

For the purpose of measuring the pressure P at increased sensitivity,the reference capacitance between the reference capacitive electrode 33and the diaphragm electrode 35 is desirably kept from being varied dueto application of any pressure to the capacitance-type pressure sensor.Nevertheless, such application of the pressure P to the diaphragmsubstrate 34 as shown in FIG. 19(B) causes the distance between thereference capacitive electrode 33 and the diaphragm electrode 35 to beslightly varied from D0 to D2, leading to a variation in referencecapacitance between the reference capacitive electrode 33 and thediaphragm electrode 35. Thus, the conventional capacitance-type pressuresensor fails to measure a pressure at increased sensitivity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a capacitance-typepressure sensor which is capable of reducing a variation in referencecapacitance.

It is another object of the present invention to provide acapacitance-type pressure sensor which is capable of reducing avariation in reference capacitance without substantially preventingdeflection of a diaphragm.

It is a further object of the present invention to provide acapacitance-type pressure sensor which is capable of facilitatingmanufacturing thereof while reducing a variation in referencecapacitance.

It is still another object of the present invention to provide acapacitance-type pressure sensor which is capable of restraining areduction in sensitivity thereof.

It Is yet another object of the present invention to provide acapacitance-type pressure sensor which is capable of ensuring removal orrelease of gas from an inside of a second pattern while restraining areduction in sensitivity.

It is a still further object of the present invention to provide acapacitance-type pressure sensor which is capable of restraining anincrease in parasitic capacity.

In accordance with the present invention, a capacitance-type pressuresensor generally includes a base substrate having a main capacitiveelectrode and a reference capacitive electrode arranged thereon in amanner to be spaced from each other at an interval, or distance, adiaphragm substrate including a diaphragm electrode arranged opposite tothe main capacitive electrode and reference capacitive electrode, and asealing insulating layer through which the base substrate and diaphragmsubstrate are joined at an outer peripheral portion thereof to eachother. The present invention further includes an insulating spacerarranged between the main capacitive electrode and the referencecapacitive electrode and coupled to the base substrate and diaphragmsubstrate. The insulating spacer has a pattern determined so as torestrain a variation in distance between the reference capacitiveelectrode and the diaphragm electrode.

When the pattern of the insulating spacer is formed so as to sealedlyclose a space between the main capacitive electrode and the diaphragmelectrode (or a space in which the main capacitive electrode ispositioned), the diaphragm is restrained from being deflected in spiteof application of a pressure to the diaphragm when air is encapsulatedin the space. Thus, the pattern of the insulating spacer is preferablyarranged so as to permit a space in which the main capacitive electrodeis positioned and that in which the reference capacitive electrode ispositioned to communicate with each other therethrough. Suchconstruction permits air to flow between the space in which the maincapacitive electrode is arranged and that in which the referencecapacitive electrode is arranged when a pressure is applied to thediaphragm, to thereby ensure deflection of the diaphragm. The insulatingspacer and sealing insulating layer may be made of an identicalinsulating material. This ensures concurrent formation of bothinsulating spacer and sealing insulating layer by printing or the likeand facilitates the formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing an example of acapacitance-type pressure sensor module having a capacitance-typepressure sensor according to the present invention incorporated therein;

FIG. 2 is a sectional view showing an embodiment of a capacitance-typepressure sensor according to the present invention;

FIG. 3 is a plan view showing a base electrode section incorporated inthe capacitance-type pressure sensor of FIG. 2;

FIG. 4 is a rear view showing a diaphragm electrode section incorporatedin the capacitance-type pressure sensor of FIG. 2;

FIG. 5 is a plan view showing a glass sealing pattern incorporated inthe capacitance-type pressure sensor of FIG. 2;

FIG. 6 is a plan view showing a glass sealing pattern formed on a baseelectrode section incorporated in the capacitance-type pressure sensorof FIG. 2;

FIG. 7A is a plan view showing a second embodiment of a capacitance-typepressure sensor according to the present invention;

FIG. 7B is a side elevation view of the capacitance-type pressure sensorshown in FIG. 7A;

FIG. 8 is a schematic sectional view of the capacitance-type pressuresensor shown in FIG. 7A;

FIG. 9 is a plan view showing a base substrate incorporated in thecapacitance-type pressure sensor shown in FIG. 7A;

FIG. 10 is a plan view showing a diaphragm substrate incorporated in thecapacitance-type pressure sensor shown in FIG. 7A;

FIG. 11 is a plan view showing a joining pattern incorporated in thecapacitance-type pressure sensor shown in FIG. 7A;

FIG. 12 is a plan view showing a pattern of a glass sealing material ona base electrode section incorporated in the capacitance-type pressuresensor shown in FIG. 7A;

FIG. 13A is a view showing an electrode pattern on a base substrateincorporated in a further embodiment of a capacitance-type pressuresensor according to the present invention;

FIG. 13B is a view showing an electrode pattern on a diaphragm substrateincorporated in the capacitance-type pressure sensor shown in FIG. 13A;

FIG. 14 is a sectional view showing electric lines of force in a leadwire section arranged in the capacitance-type pressure sensor shown inFIGS. 13A and 13B;

FIG. 15A is a plan view showing an electrode pattern on a base substratearranged in still another embodiment of a capacitance-type pressuresensor according to the present invention;

FIG. 15B is a plan view showing an electrode pattern on a diaphragmsubstrate incorporated in the capacitance-type pressure sensor of FIG.15A;

FIG. 16 is a sectional view showing electric lines of force in a leadwire section arranged in the capacitance-type pressure sensor shown inFIGS. 15A and 15B;

FIG. 17 is a view showing electrode patterns formed in yet anotherembodiment of a capacitance-type pressure sensor according to thepresent invention;

FIG. 18 is a view showing electrode patterns formed in a still furtherembodiment of a capacitance-type pressure sensor according to thepresent invention; and

FIGS. 19A and 19B each are a sectional view showing a conventionalcapacitance-type pressure sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described hereinafter with referenceto the accompanying drawings. FIG. 1 is a schematic sectional viewshowing a pressure sensor module having a capacitance-type pressuresensor of the present invention incorporated therein. The pressuresensor module, as shown in FIG. 1, generally includes a connectorassembly 21 and a pressure sensor assembly 22 on which the connectorassembly 21 is mounted. The connector assembly 21 includes a connector22 and an annular support 24 in which the connector 22 is fitted. Thepressure sensor assembly 22 includes a capacitance-type pressure sensor25, a circuit board 26 and a housing 27.

The pressure sensor module thus constructed permits fluid to be measured(hereinafter referred to as "measured fluid") such as oil or water fedthrough a high-pressure fluid feed passage 27a of a housing 27 to act apressure on a diaphragm substrate 2 of the pressure sensor 25 describedhereinafter. This permits the pressure sensor 25 to measure a variationin pressure of the measured fluid in the form of a variation incapacitance to generate a signal, which is then fed to a circuit on thecircuit board 26 on the base substrate 1 of the pressure sensor 25. Thesignal indicating a value of the pressure is processed in the circuit ofthe circuit board 26 and then fed to through a terminal member 23a ofthe connector 23 to an equipment (not shown) connected to the terminalmember 23a.

Referring now to FIG. 2, an embodiment of a capacitance-type pressuresensor according to the present invention is illustrated. Acapacitance-type pressure sensor of the illustrated embodiment generallydesignated at reference numeral 25 includes a base substrate 1 made of aceramic material and a diaphragm substrate 2, which are Joined or bondedto each other by means of a glass sealing pattern 3 made of a glassmaterial forming a sealing insulating layer.

The base substrate 1 which may be made of a ceramic plate of severalmillimeters in thickness, as detailedly shown in FIG. 3, is formed onone surface la thereof or a front surface thereof with a main capacitiveelectrode 4 and a reference capacitive electrode 5 in a manner to bespaced from each other at a predetermined interval or distance in aradial direction thereof. The main capacitive electrode 4 is made of agold paste by screen printing and formed into a thickness of 0.7 μm andan annular shape. The main capacitive electrode 4 is electricallyconnected at a part thereof to a main capacitive electrode terminal 7 bymeans of a connection section 6 made of a lead wire. The connectionsection 6 and main capacitive electrode terminal 7 may be made of a goldpaste concurrently with formation of the main capacitive electrode 4.The main capacitive electrode 4 of an annular shape has a space Sdefined at a central portion thereof, which serves to more accuratelyproportionally vary a capacitance between the main capacitive electrode4 and a first electrode section 10a of a diaphragm electrode 10depending on a pressure applied to the diaphragm substrate 2 and preventcontact between the diaphragm electrode or counter electrode 10 and themain capacitive electrode 4 due to application of a pressure of anexcessive level to the diaphragm substrate 2, to thereby preventshort-circuiting therebetween.

The reference capacitive electrode 5 is made of a gold paste by screenprinting in a manner similar to the main capacitive electrode 4. It isformed into a thickness of 0.7 μm. Also, the reference capacitiveelectrode 5 is formed into an arcuate shape so as to partially surroundthe main capacitive electrode 4 while being concentric with the maincapacitive electrode 4. The reference capacitive electrode 5 isconnected at one end thereof through a connection section 8 to areference capacitive electrode terminal 9. The connection section 8 andreference capacitive electrode terminal 9 may be made concurrently withformation of the reference capacitive electrode 5. Actually, patterns ofthe main capacitive electrode 4, reference capacitive electrode 5,connection section 6, main capacitive electrode terminal 7, connectionsection 8 and reference capacitive electrode terminal 9 may beconcurrently formed.

The diaphragm electrode or counter electrode 10 described above isformed on one surface of the diaphragm substrate 2 or a front surfacethereof as indicated at phantom lines in FIG. 4. More specifically, thediaphragm substrate 2 is made of a ceramic material and formed into athickness of 0.8 mm and the counter electrode 10 is made of a gold pasteby screen printing. The counter electrode 10 is formed into a thicknessof 0.7 μm. Also, the counter electrode 10 includes a second electrodesection 10b as well as the first electrode section 10a briefly describedabove. The first electrode section 10a is formed into a circular shapein a manner to be opposite to the main capacitive electrode 4 and thesecond electrode section 10b is formed into an arcuate shape in a mannerto be opposite to the reference capacitive electrode 5. The secondelectrode section 10b is connected at one end thereof to a counterelectrode terminal 11 and likewise the first electrode section 10a iselectrically connected at a part thereof to the counter electrodeterminal 11 through a connection section 12. The counter electrode 10,counter electrode terminal 11 and connection section 12 may beconcurrently formed by single screen printing. In the illustratedembodiment, the glass sealing pattern 3 is formed into a thickness whichpermits a distance between the first electrode section 10a and the maincapacitive electrode 4 and that between the second electrode section 10band the reference capacitive electrode 5 to be about 10 μm.

The joining pattern or glass sealing pattern 3 is made of an insulatingmaterial mainly consisting of glass and, as detailedly shown in FIG. 5,includes a sealing insulating layer (first pattern) 3a, an insulatingspacer (second pattern) 3b and connection sections 3c to 3f. The sealinginsulating layer 3a is formed into an annular shape so as to permit thebase substrate 1 and diaphragm substrate 2 to be joined at an outerperipheral portion thereof to each other therethrough. Moreparticularly, the sealing insulating layer 3a is positioned outside thereference capacitive electrode 5 to surround the reference capacitiveelectrode 5, to thereby join the base substrate 1 and diaphragmsubstrate 2 to each other while defining a predetermined interval or gapbetween a front surface of the base substrate 1 and that of thediaphragm substrate 2. Also, the insulating spacer 3b is arrangedbetween the main capacitive electrode 4 and the reference capacitiveelectrode 5 and coupled to the base substrate 1 and diaphragm substrate2. The insulating spacer 3b is formed into dimensions and aconfiguration which restrain a variation in distance between thereference capacitive electrode 5 and the counter electrode 10 or preventa distance between the reference capacitive electrode 5 and the counterelectrode 10 from being substantially varied. More specifically, theinsulating spacer 3b includes a first spacer half 3b1 of a semi-annularshape and a second spacer half 3b2 of a semi-annular shape which arearranged opposite to each other, to thereby cooperate with each other tosubstantially form a circle while defining slits S1 and S2 therebetweenwhich permit a space in which the main capacitive electrode 4 ispositioned and that wherein the reference capacitive electrode 5 ispositioned to communicate with each other therethrough.

It was confirmed that the capacitance-type pressure sensor of theillustrated embodiment reduces a variation in distance between thereference capacitive electrode 5 and the second electrode section 10b ofthe counter electrode 10 to a level one fortieth (1/40) (1/40) tofiftieth (1/50) (1/50) as compared with that of a capacitance-typepressure sensor free from any insulating spacer. Arrangement of theinsulating spacer 3b causes the diaphragm substrate 2 to be increased inresistance to deflection. However, such a problem may be solved byreducing a thickness of the diaphragm substrate 2 to suitably adjustflexibility of the diaphragm substrate 2. Instead, it may be solved bymaking the diaphragm substrate 2 of any other suitable material. Theconnection sections 3c to 3f are arranged so as to radially extend fromthe second spacer half 3b2 toward the sealing insulating layer 3a toconnect the second spacer half 3b2 and sealing insulating layer 3a toeach other therethrough. The counter electrode terminal 11 is arrangedin a manner to be enclosed with the second spacer half 3b2, connectionsection 3c, sealing insulating layer 3a and connection section 3d. Themain capacitive electrode terminal 7 is enclosed with the second spacerhalf 3b2, connection section 3d, sealing insulating layer 3a andconnection section 3e. Also, the reference capacitive electrode terminal9 is enclosed with the second spacer half 3b2, connection section 3e,sealing insulating layer 3a and connection section 3f.

In the illustrated embodiment, firstly the base substrate 1 anddiaphragm substrate 2 are formed on the front surface thereof with theelectrodes 4, 5 and 10 by printing or sputtering. Then, a mask having apredetermined mask pattern is arranged on the front surface of the basesubstrate 1, resulting in a glass sealing material pattern 3' beingformed of a molten glass sealing material by screen printing, as shownin FIG. 6. Subsequently, the diaphragm 2 is superposed on the basesubstrate 1 through the glass sealing material 3' cured while keepingthe electrodes 4 and 5 and the electrode 10 opposite to each other.Thereafter, the substrates 1 and 2 thus superposed on each other areplaced in an oven to melt the glass sealing material pattern 3' to jointhe base substrate 1 and diaphragm substrate 2 to each other through theglass sealing pattern 3 to each other, resulting in the capacitance-typepressure sensor being completed.

Patterning of the insulating spacer 3b in a manner to close the spacebetween the main capacitive electrode 4 and the diaphragm electrode 10(or the space in which the main capacitive electrode is positioned)causes the diaphragm substrate 2 to be hard to deflect or bend due toapplication of a pressure to the diaphragm substrate 2, when air isencapsulated in the space. In order to avoid the problem, theillustrated embodiment is so constructed that the pattern of theinsulating spacer 3b is formed with two such slits S1 and S2 (FIG. 5),resulting in the space in which the main capacitive electrode 4 isarranged and that in which the reference capacitive electrode 5 ispositioned communicating with each other therethrough. Such constructionpermits air to move between both spaces when a pressure is applied to arear surface of the diaphragm 2, so that the problem that the diaphragmis hard to deflect may be eliminated.

In the illustrated embodiment, the insulating spacer 3b is formed of twosemi-annular spacer halves 3b1 and 3b2 while being spaced from eachother at a predetermined interval, or distance resulting in beingprovided with two such slits S1 and S2. However, the present inventionis not limited to such construction. The number of slits and aconfiguration of the insulating spacer may be suitably selected, so longas the diaphragm substrate 2 is permitted to deflect due to applicationof a pressure thereto and a variation in distance between the referencecapacitive electrode 5 and the counter electrode 10 can be restrained.

Also, In the illustrated embodiment, the sealing insulating layer 3a andinsulating spacer 3b are formed of the glass sealing pattern 3. Instead,the sealing insulating layer 3a and insulating spacer 3b may be made ofa ceramic material, a resin material or the like. Use of the samematerial for the insulating spacer 3b and sealing insulating layer 3aensures concurrent formation of the insulating spacer 3b and sealinginsulating layer 3a by printing or the like and facilitates theformation. Nevertheless, it is a matter of course that the sealinginsulating layer 3a and insulating spacer 3b may be made of materialsdifferent from each other.

Further, the above-described formation of the diaphragm electrode 10 inthe manner that the first electrode section 10a and second electrodesection 10b are respectively opposite to the main capacitive electrode 4and reference capacitive electrode 5 permits the insulating spacer 3b tobe joined to a portion of the front surface of the diaphragm substrate 2exposed between the first electrode section 10a and the second electrodesection 10b. This ensures firm coupling of the insulating spacer 3b tothe diaphragm substrate 2.

Arrangement of the insulating spacer 3b between the main capacitiveelectrode 4 and the reference capacitive electrode 5 to couple the basesubstrate 1 and diaphragm substrate 2 to each other in the illustratedembodiment permits the diaphragm substrate 2 to be deflected in a spacedefined in the insulating spacer 3b, resulting in restraining avariation in distance between the reference capacitive electrode 5 andthe second electrode section 10b of the counter electrode 10 due toapplication of a pressure to the diaphragm substrate 2. This reduces avariation in capacitance between the reference capacitive electrode 5and the counter electrode (10b), to thereby increase accuracy with whichthe pressure is measured.

As a result of examining characteristics of the capacitance-typepressure sensor of the illustrated embodiment actually manufactured, itwas found that the pressure sensor has sensitivity of a level lower thana theoretical value. The cause was studied. As a result, it was revealedthat the second pattern or insulating spacer 3b of the joining patternor glass sealing pattern 3 intersects the connection section or leadwire section 6 of the main capacitive electrode 4, to thereby reducesensitivity of the pressure sensor. Sensitivity of the pressure sensoror sensitivity of a main capacity is defined to be (variation ΔCn incapacitance at a certain pressure)/(initial value Co). The initial valuecan be regarded as a sum (Cm+Cx) of a main capacity Cm obtained betweenthe main capacitive electrode 4 and the first electrode section 10a ofthe counter electrode 10 when no pressure is applied to the sensor and acapacity Cx obtained between the lead wire section 6 and the firstelectrode section 10a of the counter electrode 10. Unfortunately, aninsulating material such as a glass material used for the insulatingspacer 3b is increased in dielectric constant, so that the capacity Cxis increased at an intersection between the insulating spacer 3b and thelead wire section 6. This results in a denominator of theabove-described expression being increased, to thereby reducesensitivity of the pressure sensor.

Referring now to FIGS. 7A to 12, another embodiment of acapacitance-type pressure sensor according to the present invention isillustrated, which is constructed so as to solve the above-describedproblem. In a capacitance-type pressure sensor of the illustratedembodiment, an insulating spacer 113 is arranged so as to be kept fromintersecting a lead wire section 106 connected to a main capacitiveelectrode 104. Such construction keeps the lead wire section 106 and acounter electrode 110 from facing each other through the insulatingspacer 113 inherently increased in dielectric constant, to therebypermit a reduction in capacity Cx between the lead wire section 106 andthe counter electrode 110, resulting in preventing a reduction insensitivity of the pressure sensor.

The capacitance-type pressure sensor of the illustrated embodiment, asschematically shown in FIGS. 7 and 8, is so constructed that a basesubstrate 101 and a diaphragm substrate 102 are coupled to each otherthrough a glass sealing pattern 103. The glass sealing pattern 103 isactually formed into a highly reduced thickness. In FIG. 8, a thicknessof the glass sealing pattern 103 and an interval between the basesubstrate 101 and the diaphragm substrate 102 are exaggeratedly shown.The base substrate 101 is made of a ceramic material and formed into asubstantially cylindrical shape. The base substrate 101 has a cut endsurface or a side surface of which a part is cut into a flat shape asindicated at reference character 101a in FIG. 7(A). The base substrate101 is formed on a surface thereof opposite to a surface thereof facingthe diaphragm substrate 102 with a signal circuit (not shown). The basesubstrate 101 is formed on the surface thereof facing the diaphragmsubstrate 102 with the main capacitive electrode 104 and a referencecapacitive electrode 105 in a manner to be spaced from each other at aninterval distance in a radial direction thereof. The main capacitiveelectrode 104 is made of a gold (Au) paste by screen printing and formedinto a thickness of 0.7 μm and an annular shape. The main capacitiveelectrode 104 is electrically connected at a part thereof through thelead wire section 106 to a main capacitive electrode terminal 107. Thelead wire section 106 is formed into a width which is set to be smallerthan that (1 mm) of a lead wire section 108 connected to the referencecapacitive electrode 105 and so as to prevent tan δ determined by both amain capacitance between the main capacitive electrode 104 and thecounter electrode 110 and a resistance value containing a resistance ofthe lead wire section 106 from being excessively increased. In theillustrated embodiment, the lead wire section 106 is formed into a widthof from 0.4 to 0.6 mm. Also, the lead wire section 106 is formed into alength of 5.4 mm.

The lead wire section 106 and main capacitive electrode terminal 107 maybe formed of a gold (Au) paste concurrently with formation of the maincapacitive electrode 104. The reference capacitive electrode 105 is madeof an Au paste by screen printing as in the main capacitive electrode104 and formed into a thickness of 0.7 μm. The reference capacitiveelectrode 105 is formed into an arcuate shape in a manner to beconcentric with the main capacitive electrode 104 and partially surroundthe main capacitive electrode 104 while being kept from intersecting thelead wire section 106. The reference capacitive electrode 105 isconnected at one end thereof through the lead wire section 108 to areference capacitive electrode terminal 109. The reference capacitiveelectrode terminal 109 is likewise made concurrently with formation ofthe reference capacitive electrode 105. Actually, patterns of the maincapacitive electrode 104, reference capacitive electrode 105, lead wiresections 106 and 108, main capacitive electrode terminal 107, andreference capacitive electrode terminal 109 are concurrently formed. Themain capacitive electrode terminal 107 and reference capacitiveelectrode terminal 109 are electrically connected through conductiveconnection sections C1 and C2 to a signal circuit (not shown) formed onthe surface 101b of the base substrate 101 (FIGS. 7A and 7B). Theconductive connection sections C1 and C2 are formed of a conductivepaste on the cut end surface 101a of the base substrate 101.

The diaphragm substrate 102 is made of a ceramic material and formedinto a thickness of 0.46 mm and a circular shape. The diaphragmsubstrate 102 is formed on a surface thereof opposite to the basesubstrate 101 with the counter electrode 110 as shown in FIG. 10. Thecounter electrode 110 is made of an Au paste by screen printing andformed into a thickness of 0.7 μm. The counter electrode 110 is formedinto a circular shape and arranged opposite to the main capacitiveelectrode 104, lead wire section 106 and reference capacitive electrode105 formed on the base substrate 101 while being spaced therefrom atpredetermined intervals. The counter electrode 110 has a connectionterminal 111 radially outwardly projected from a part thereof. Thecounter electrode 110 and connection terminal 111 are concurrentlyformed by one-time or single screen printing. The connection terminal111 is electrically connected to the signal circuit (not shown) formedon the surface 101b of the base substrate 101 through a conductiveconnection section C3 formed of a conductive paste on the cut endsurface 101a of the base substrate 101, as shown in FIGS. 7A and 7B.

The glass sealing pattern 103 is made of an insulating material (joiningmaterial) mainly consisting of glass and formed into a thickness of 10to 15 μm. The glass sealing pattern 103, as shown in FIGS. 8 and 11,includes a first pattern 112 acting as an insulating sealing layer and asecond pattern 113 acting as an insulating spacer. The first pattern 112is arranged outside the reference capacitive electrode 105 so as tosurround the reference capacitive electrode 105 and formed into a shapecorresponding to a contour of the base substrate 101 so as to intersectthe two lead wire sections 106 and 108. Also, the first pattern 112includes an inner peripheral edge 112a and an outer peripheral edge 112bwhich are connected to each other through connection pattern sections112c. Such construction of the glass sealing pattern 103 prevents anyvoid (crack) from being formed in the glass sealing pattern 103 duringformation of the pattern 103.

The second pattern 113 is arranged between the main capacitive electrode104 and the reference capacitive electrode 105, to thereby restrain avariation in interval or distance between the base substrate 101 and thediaphragm substrate 102 which occurs between the reference capacitiveelectrode 105 and the counter electrode 110. The second pattern 113 isformed into a substantially annular shape and is provided at a partthereof with a cutout 113a at which continuity of the second pattern 113is interrupted. The cutout 113a acts to permit the lead wire section 106connected to the main capacitive electrode 105 to extend therethroughwithout being contacted with the second pattern 113. The cutout 113 alsoacts as a vent passage which permits gas in the second pattern 113 to beremoved therefrom.

Such arrangement of the cutout 113a at the intersection between theglass sealing material pattern 103 and the second pattern (insulatingspacer) 113 as shown in FIG. 12 prevents the lead wire section 106 andcounter electrode 110 from facing each other through the glass sealingpattern 103 inherently increased in dielectric constant, to therebyadvantageously reduce a capacity between the lead wire section 106 andthe counter electrode 110, resulting in restraining a reduction insensitivity of the pressure sensor. The capacitance-type pressure sensorof the illustrated embodiment may be manufactured in substantially thesame manner as the first embodiment described above. The conductiveconnection sections C1 to C3 may be made of a conductive paste such as asilver paste or the like subsequent to joining between the basesubstrate 101 and the diaphragm substrate 102.

Samples 1 to 4 of various capacitance-type pressure sensors weremanufactured for measuring an initial value of the pressure sensor andsensitivity thereof. Sample 1 was manufactured according to theconstruction of the illustrated embodiment. Sample 2 was constructed inthe same manner as Sample 1 except that the lead wire section 106 hasthe same width (1 mm) as that in Sample 1. Thus, Sample 2 is included inthe scope of the present invention. Sample 3 was constructed in the samemanner as Sample 1 except that the cutout 113a is not formed and thelead wire section 106 has the same width (1 mm) as that in Sample 1.Sample 4 was constructed in the same manner as Sample 1 except that thecutout 113a is not provided. Results of the measurement were as shown inTable 1.

                  TABLE 1                                                         ______________________________________                                        Sample No.     Initial Value                                                                           Sensitivity                                          ______________________________________                                        1              20        6                                                    2                                         5                                   3                                         4                                   4                                         4.5                                 ______________________________________                                    

Table 1 indicates that the capacitance-type pressure sensors of Samples1 and 2 are reduced in initial value, to thereby be increased insensitivity, as compared with those of Samples 3 and 4. In particular,the capacitance-type pressure sensor of Sample 4 in which the lead wiresection 106 is decreased in width is increased in sensitivity ascompared with that of Sample 3, however, it is reduced in sensitivity ascompared with Samples 1 and 2.

In the illustrated embodiment, the lead wire section 106 is formed intoa width smaller than that of the lead wire section 108. However, it maybe formed into any other suitable width.

The illustrated embodiment, as described above, is so constructed thatthe second pattern 115 is formed into a substantially annular shape ofwhich continuity is interrupted by the cutout 113a which keeps the leadwire section 106 connected to the main capacitive electrode 104 fromdirectly intersecting the second pattern 113 and more specificallypermits the lead wire section 106 to intersect the second pattern 113without being contacted with the second pattern 113. Such construction,as described above, also permits the cutout 113a to act as a ventpassage as well. Lack of the cutout or vent passage 113a deterioratesdeformation or deflection of the diaphragm when a pressure is appliedthereto.

The lead wire section 106 connected to the main capacitive electrode 104is preferably formed into a width smaller than that of the lead wiresection 108 connected to the reference capacitive electrode 105.Intersection between the second pattern 113 and the lead wire section106 through the cutout 113a while keeping both from being contacted witheach other results in the capacity Cx being reduced. The capacity Cx isfurther reduced when the lead wire section 106 opposite to the counterelectrode 110 is reduced in width. Thus, the pressure sensor is furtherincreased in sensitivity. However, an excessive reduction in width ofthe lead wire section 106 causes an increase in resistance of the leadwire section 106, resulting in tan δ determined depending on a maincapacitance and a resistance of the lead wire sections being excessivelyincreased, leading to an increase in energy loss. Thus, it is requiredthat the lead wire section 106 is formed into a width reduced whilepreventing an excessive increase of tan δ. More specifically, when thelead wire section connected to the main capacitive electrode is formedinto a width of 0.4 to 0.6 mm, the sensitivity is increased whilepreventing an excessive increase of tan δ.

In the present invention, patterns of the main capacitive electrode,reference capacitive electrode and counter electrode may be determinedas desired. For example, the patterns may be determined in such a manneras shown in FIGS. 13A and 13B, which shows a further embodiment of acapacitance-type pressure sensor according to the present invention,wherein reference numerals correspond to the reference numeralsdiscussed in the embodiment described above with reference to FIGS. 1 to6, except with an additional prefix of 200. In a capacitance-typepressure sensor of the illustrated embodiment, a lead wire section 212which is a connection section on a side of a counter electrode 210 ispositioned between a lead wire section 206 which is a connection sectionconnected to a main capacitive electrode 204 and a lead wire section 208which is a connection section connected to a reference capacitiveelectrode 205 while keeping a base substrate 201 and a flexiblesubstrate 202 joined to each other. An insulating spacer 203b isarranged so as to be kept from directly intersecting the lead wiresection or the connection section extending from the main capacitiveelectrode 204 or so as to intersect the lead wire section without beingdirectly contacted therewith.

When a pressure of oil, water or the like is to be measured by thecapacitance-type pressure sensor of the illustrated embodiment, firstlya pressure of fluid such as oil, water or the like is applied to a rearsurface of the diaphragm substrate 202, to thereby deflect the diaphragmsubstrate 202, leading to a variation in capacitance between the maincapacitive electrode 204 and a first electrode section 210a of thecounter electrode 210. Then, the pressure is calculated on the basis ofa main capacitance between the main capacitive electrode 204 and thefirst electrode section 210a and a reference capacitance between thereference capacitive electrode 205 and the second electrode section210b. However, the capacitance-type pressure sensor of the illustratedembodiment causes an increase in parasitic capacity between the leadwire sections 206, 208 and the lead wire section 212, leading toaddition of the parasitic capacity to the capacity measured on the basisof the main capacitance and reference capacitance, resulting in anyerror occurring in the pressure of fluid measured. Now, the reasons whythe parasitic capacity is increased will be considered hereinafter. FIG.14 is a sectional view of a portion of the capacitance-type at which thelead wire section 212 of FIG. 13(B) and the lead wire sections 206 and208 of FIG. 13(A) correspond to each other. The lead wire section 212and lead wire sections 206 and 208, as shown in FIGS. 13(A) and 13(B),are arranged in a manner to be obliquely opposite to each other (or in amanner to alternate with each other). On the rear surface of thediaphragm substrate 202 exists measured fluid E which is constituted bya dielectric substance such as oil or the like or a conductive substancesuch as water or the like. In the capacitance-type pressure sensor thusconstructed, electric lines of force D1 outwardly discharged from thelead wire section 212 are caused to partially return through themeasured fluid E to the lead wire sections 206 and 208 arrangedobliquely opposite to the lead wire section 212. Thus, it would beconsidered that when the measured fluid E is a dielectric substance, thesubstance increased in dielectric constant exists between the lead wiresections 206, 208 and the lead wire section 212, leading to an increasein parasitic capacity. When the measured fluid E is a conductivesubstance such as water or the like, the electric lines of force D1would pass through the conductive substance, so that a part of theelectric lines of force D1 is deformed or bent, to thereby return to thelead wire sections 206 and 208 through a highly reduced distance,leading to an increase in parasitic capacity between the lead wiresections 206, 208 and the lead wire section 212.

FIGS. 15(A) and 15(B) show an electrode pattern of a base substrate 301and that of a diaphragm substrate 302 which are incorporated in stillanother embodiment of a capacitance-type pressure sensor according tothe present invention, respectively. A capacitance-type pressure sensorof the illustrated embodiment is constructed so as to reduce the affectcaused due to an increase in parasitic capacity. The base substrate 301is made of a ceramic material and is formed on a surface thereofopposite to the diaphragm substrate 302 with a main capacitive electrode304, a reference capacitive electrode 305, and two lead wire sections306 and 308. The main capacitive electrode 304 is made of a gold pasteby screen printing and formed into an annular shape. Also, the maincapacitive electrode 304 is formed into a thickness of 0.7 μm and adiameter of 7.8 mm. The reference capacitive electrode 305 is made of agold paste by screen printing, like the main capacitive electrode 304.The reference capacitive electrode 305 is formed into a thickness of 0.7μm and an outer diameter of 15 mm. Also, the reference capacitiveelectrode 305 is formed into an arcuate shape so as to partiallysurround the main capacitive electrode 304. The first lead wire section306 is connected to the main capacitive electrode 304 and the secondlead wire section 308 is connected to one end of the referencecapacitive electrode 305. The lead wire sections 306 and 308 arearranged so as to extend in juxtaposition to each other toward an outerperipheral portion of the base substrate 301 and have ends serving asterminal sections 307 and 309, respectively.

The diaphragm substrate 302 is made of an insulating ceramic materialwhich permits it to be deflected depending on a pressure of fluidapplied to the diaphragm substrate 302 when the pressure is applied to arear surface of the substrate 302. The diaphragm substrate 302 is soarranged that the rear surface thereof is opposite to a bottom surface27b1 of a pressure sensor receiving chamber 27b of a housing 27 throughboth an O-ring 28a shown in FIG. 1 and a backup ring 28b arrangedoutside the O-ring 28a in a manner to be concentric with the O-ring 28a.The diaphragm substrate 302 is provided on a front surface thereof or asurface thereof opposite to the base substrate 301 with a counterelectrode (movable-side electrode pattern) 310 and a terminal(movable-side terminal pattern) 311 as shown in FIG. 15(B). The counterelectrode 310 is made of a gold paste by screen printing. The counterelectrode 310 is constituted by a disc-like electrode pattern of 0.7 μmin thickness and 18.6 mm in diameter. Also, the counter electrode isformed into a size sufficient to reduce an increase in parasiticcapacity occurring due to existence of measured fluid such as oil orwater on the rear surface of the diaphragm substrate 302. Morespecifically, it is formed into a size somewhat larger than a regioncorresponding to an oil adhering range (or a range surrounded by theO-ring 28 of FIG. 1) and formed into a diameter corresponding to asubstantial part of the two lead wire sections 306 and 308 of the basesubstrate 301 other than the terminal sections 307 and 309.

The terminal section 311 is arranged so as to extend from the counterelectrode 310 toward an outer peripheral portion of the diaphragmsubstrate 302. Also, the terminal section 311 includes an extensionwhich is arranged so as to extend along the lead wire sections 306 and308. However, the extension of the terminal section 311 is out of theoil adhering range (or the range surrounded by the O-ring 28 of FIG. 1),resulting in preventing the parasitic capacity from being substantiallyincreased.

In the capacitance-type pressure sensor of the illustrated embodiment,fluid (water or oil) flowing through the high-pressure fluid feedpassage 27a shown in FIG. 1 causes a pressure to be applied to the rearsurface of the diaphragm substrate 302, to thereby deflect the diaphragmsubstrate 302, leading to a variation in interval or distance betweenthe main capacitive electrode 304 and the counter electrode 310,resulting in a variation in capacitance between the main capacitiveelectrode 304 and the counter electrode 310.

In the capacitance-type pressure sensor of the illustrated embodiment,the lead wire sections 306 and 308 and the counter electrode having anarea substantially larger than the lead wire sections 306 and 308 arearranged so as to be opposite to each other at a portion of the pressuresensor corresponding to a position at which the measured fluid E such asoil (dielectric substance) or water (conductive substance) exists. Inother words, a portion of the counter electrode 310 opposite to the leadwire sections 306 and 308 constitutes a parasitic capacity increaserestraining electrode section for restraining an increase in parasiticcapacity. Thus, a distance by which electric lines of force D outwardlydischarged from the parasitic capacity increase restraining electrodesection of the counter electrode 310 opposite to the lead wire sections306 and 308 return to the lead wire sections 306 and 308 through themeasured fluid E is caused to be considerably increased. This results inthe parasitic capacity being highly reduced. In particularly, anincrease in distance by which ends 310a of the parasitic capacityincrease restraining electrode section exceed outer ends 306a and 308aof the lead wire sections 306 and 308 leads to an increase in distanceof the electric lines of force.

The capacitance-type pressure sensor (Sample 11) of the illustratedembodiment shown in FIG. 15 and the capacitance-type pressure sensor(Sample 12) having the electrode pattern shown in FIG. 13 were subjectto a test for measuring a variation to a capacity value 25 pF whilekeeping oil (dielectric substance) or water (conductive substance) inthe same amount existing on a portion of the rear surface of thediaphragm substrate corresponding to the lead wire sections. Thecapacitance-type pressure sensor having the electrode pattern shown inFIG. 13 is constructed in substantially the same manner as thecapacitance-type pressure sensor of the illustrated embodiment shown inFIG. 15 except the counter electrode. The results were as shown in Table2.

                  TABLE 2                                                         ______________________________________                                                    Capacity Variation (pF)                                           Sample        Water     Oil                                                   ______________________________________                                        11            +0.1      +0.05                                                 12                           +0.73                                            ______________________________________                                    

Table 2 indicates that the capacitance-type pressure sensor of theillustrated embodiment restrains an increase in parasitic capacity dueto existence of oil (dielectric substance) or water (conductivesubstance) on the rear surface of the diaphragm substrate, to therebyreduce a variation in capacity (error).

Formation of the disc-like electrode pattern while increasing a diameterof the counter electrode in the embodiment shown in FIG. 15 permits theparasitic capacity increase restraining electrode section to be formedaround a whole circumference thereof, to thereby positively restrain anincrease in parasitic capacity even when positional relationship betweenthe base substrate and the diaphragm substrate opposite to each other isdeviated. This facilitates positioning between the fixed-side substrateand the movable-side substrate.

Referring now to FIG. 17, an electrode pattern of a capacitance-typepressure sensor 425 of yet another embodiment according to the presentinvention is illustrated. In connection with the illustrated embodiment,reference numerals correspond to the reference numerals discussed in theembodiment of FIG. 15, except with an additional prefix of 400. Thecapacitance-type pressure sensor 425 of the illustrated embodiment isconstructed in substantially the same manner as the capacitance-typepressure sensor of FIG. 15 except a counter electrode 410. In FIG. 17, amain capacitive electrode 404, a reference capacitive electrode 405 andlead wire sections 406 and 408 formed on a base substrate are indicatedat solid lines and the counter electrode 410 provided on a diaphragmsubstrate in a manner to be opposite the electrodes 404 and 405 and leadwire sections 406 and 408 on the base substrate are indicated at brokenlines for the sake of brevity. In the illustrated embodiment, thecounter electrode 410 includes a disc-like electrode pattern 410a and aparasitic capacity increase restraining electrode section 410bcorresponding to the main capacitive electrode 404 and referencecapacitive electrode 405. The parasitic capacity increase restrainingelectrode section 410b is formed so as to arcuately project from thedisc-like electrode pattern 410a in a manner to be entirely opposite toone region on a front surface of the base substrate on which the leadwire sections 406 and 408 are formed. An insulating space (not shown)may be of course arranged in the illustrated embodiment as well.However, it is not necessarily required to combine a concept that theparasitic capacity increase restraining electrode section is arranged toreduce the parasitic capacity with a concept that the insulating spaceris arranged.

Referring now to FIG. 18, a capacitance-type pressure sensor 525 of astill further embodiment of the present invention and a counterelectrode 510 are illustrated. The capacitance-type pressure sensor ofthe illustrated embodiment is constructed in substantially the samemanner as the capacitance-type pressure sensor of FIG. 15 except thecounter electrode 510. In the illustrated embodiment, the counterelectrode 510 includes a first electrode section 510a corresponding to amain capacitive electrode 504, a second electrode section 510bcorresponding to a reference capacitive electrode 505, and a parasiticcapacity increase restraining electrode section 510c. The parasiticcapacity increase restraining electrode section 510c is formed so as toproject from the first electrode section 510a in a manner to be entirelyopposite to one region on a front surface of a base substrate on whichlead wire sections 506 and 508 are formed, like the parasitic capacityincrease restraining electrode section 410b shown in FIG. 17. In otherwords, the counter electrode 510 corresponds to a combination of thecounter electrode 210 shown in FIG. 13(B) with the parasitic capacityincrease restraining electrode section 510c. An insulating spacer is ofcourse arranged in the illustrated embodiment as well. Also, as in theembodiment described above with reference to FIG. 17, a concept that theparasitic capacity increase restraining electrode section is arranged toreduce the parasitic capacity is not necessarily required to be combinedwith a concept that the insulating spacer is arranged.

In each of the embodiments shown in FIGS. 15, 17 and 18, the parasiticcapacity increase restraining electrode section is arranged on a side ofthe diaphragm substrate. Such arrangement permits electric lines offorce discharged from the parasitic capacity increase restrainingelectrode section to return through a dielectric substance such as oilor a conductive substance such as water (fluid of which a pressure is tobe measured) existing on a rear surface of the diaphragm substrate tothe lead wire sections (306, 308 and the like) on the base substrate,resulting in a distance by which the electric lines of force pass beingconsiderably increased. Such an increase in the distance significantlyreduces the affect caused due to an increase in parasitic capacity evenwhen the electric lines of force pass through the dielectric substance.Also, it reduces the number of electric lines of force returning througha reduced distance, to thereby restrain an increase in parasiticcapacity, even when the electric lines of force pass through theconductive substance. Thus, the embodiments each effectively restrainoccurrence of an error in measurement of a pressure of the fluid.

The parasitic capacity increase restraining electrode section issummarized as follows:

For example, the parasitic capacity increase restraining electrode maybe constructed by extending the counter electrode toward the outerperipheral portion of the diaphragm substrate to render it opposite tothe lead wire sections on the base substrate, to thereby restrain anincrease in parasitic capacity. In order to restrain an increase inparasitic capacity when the counter electrode is thus extended to permitthe parasitic capacity increase restraining electrode section to beconstituted by the counter electrode, a size (area) of the parasiticcapacity increase restraining electrode section and a configurationthereof are determined so that a distance by which electric lines offorce discharged from the parasitic capacity increase restrainingelectrode section return through the dielectric substance or conductivesubstance positioned on the rear surface of the diaphragm substrate tothe lead wire sections on the base substrate is increased sufficient toreduce a reduction in parasitic capacity. The size and configuration arevaried depending on a size and a configuration of the lead sire sectionson the base substrate. In particular, an increase in length or distanceby which an outer end of the parasitic capacity increase restrainingelectrode section extends beyond an end of the lead wire sections on thebase substrate leads to an increase in distance of the electric lines offorce.

The parasitic capacity increase restraining electrode section may beconnected to the counter electrode provided on the diaphragm substrate.Alternatively, it may not be connected to the counter electrode. Thus,the parasitic capacity increase restraining electrode section may beelectrically independent or insulated from the counter electrode.

In general, a parasitic capacity is remarkably increased in acapacitance-type pressure sensor including a diaphragm substrate havinga pressure of fluid increased in dielectric constant or conductivityapplied to a rear surface thereof or a capacitance-type pressure sensorfor measuring a pressure of fluid such as water. Also, a parasiticcapacity is apt to be increased in a capacitance-type pressure sensorincluding a base substrate on which a plurality of lead wire sectionsare arranged. Application of the present invention to a capacitance-typepressure sensor in which a parasitic capacity is apt to be increasedpermits it to exhibit advantages of the present invention.

Industrial Applicability

Arrangement of the insulating spacer between the main capacitiveelectrode and the reference capacitive electrode to couple the basesubstrate and diaphragm substrate to each other permits a portion of thediaphragm surrounded by the insulating spacer to be deflected, resultingin restraining a variation in distance between the reference capacitiveelectrode and the diaphragm electrode due to application of a pressureto the diaphragm. This permits a variation in capacitance between thereference capacitive electrode and the diaphragm electrode, to therebyincrease accuracy at which the pressure is measured.

We claim:
 1. A capacitance-type pressure sensor comprising:a basesubstrate having a main capacitive electrode and a reference capacitiveelectrode arranged thereon in a manner to be spaced a distance from eachother; a diaphragm substrate including a diaphragm electrode arrangedopposite to said main capacitive electrode and reference capacitiveelectrode; a sealing insulating layer through which said base substrateand diaphragm substrate are joined at an outer peripheral portionthereof to each other; and an insulating spacer arranged between saidmain capacitive electrode and said reference capacitive electrode andcoupled to said base substrate and diaphragm substrate; said insulatingspacer having a pattern determined so as to restrain a variation indistance between said reference capacitive electrode and said diaphragmelectrode.
 2. A capacitance-type pressure sensor as defined in claim 1,wherein said insulating spacer is arranged so as to be kept from beingcontacted with said main capacitive electrode and reference capacitiveelectrode.
 3. A capacitance-type pressure sensor as defined in claim 1,wherein said pattern of said insulating spacer is arranged so as topermit a space in which said main capacitive electrode is positioned andthat in which said reference capacitive electrode is positioned tocommunicate with each other therethrough.
 4. A capacitance-type pressuresensor as defined in claim 1, wherein said insulating spacer and sealinginsulating layer are made of an identical insulating material.
 5. Acapacitance-type pressure sensor comprising:a base substrate made of aceramic material and provided on one surface thereof with a maincapacitive electrode of an annular shape, a lead wire section connectedto said main capacitive electrode, a reference capacitive electrode ofan arcuate shape arranged outside said main capacitive electrode in amanner to be kept from intersecting said lead wire section and a leadwire section connected to said reference capacitive electrode; adiaphragm substrate made of a ceramic material and provided on onesurface thereof with a counter electrode in a manner to be spaced fromsaid main capacitive electrode and reference capacitive electrode at apredetermined distance; and a joining pattern made of an insulatingmaterial mainly consisting of glass and arranged between said basesubstrate and said diaphragm substrate to join said base substrate anddiaphragm substrate to each other while defining said predetermineddistance between said base substrate and said diaphragm substrate; saidjoining pattern including a first pattern and a second pattern, saidfirst pattern being arranged outside said reference capacitive electrodeto surround said reference capacitive electrode and intersecting saidlead wire sections, said second pattern being positioned between saidmain capacitive electrode and said reference capacitive electrode toprevent said predetermined distance between said base substrate and saiddiaphragm substrate from being varied between said reference capacitiveelectrode and said counter electrode; said second pattern being formedinto an annular shape while being formed with a cutout which permitssaid lead wire section connected to said main capacitive electrode topass therethrough without being contacted with said second pattern.
 6. Acapacitance-type pressure sensor comprising:a base substrate provided onone surface thereof with a main capacitive electrode, a lead wiresection connected to said main capacitive electrode, a referencecapacitive electrode arranged outside said main capacitive electrode,and a lead wire section connected to said reference capacitiveelectrode; a diaphragm substrate provided on one surface thereof with acounter electrode in a manner to be spaced from said main capacitiveelectrode, lead wire section and reference capacitive electrode at apredetermined distance; a sealing insulating layer made of an insulatingmaterial and arranged between said base substrate and said diaphragmsubstrate and outside said reference capacitive electrode to surroundsaid reference capacitive electrode and join said base substrate anddiaphragm substrate to each other while defining said predetermineddistance between said one surface of said base substrate and said onesurface of said diaphragm substrate; and an insulating spacer arrangedbetween said main capacitive electrode and said reference capacitiveelectrode to restrain said predetermined distance between said basesubstrate and said diaphragm substrate from being varied between saidreference capacitive electrode and said counter electrode; saidinsulating spacer being arranged so as to be kept from intersecting saidlead wire connected to said main capacitive electrode.
 7. Acapacitance-type pressure sensor as defined in claim 6, wherein saidlead wire section connected to said main capacitive electrode has awidth smaller than that of said lead wire section connected to saidreference capacitive electrode.
 8. A capacitance-type pressure sensor asdefined in claim 6, wherein said lead wire section connected to saidmain capacitive electrode has a width set within a range of from 0.4 to0.6 mm.
 9. A capacitance-type pressure sensor as defined in claim 6,wherein said diaphragm substrate is provided on said one surface thereofwith a parasitic capacity increase restraining electrode section forrestraining an increase of a parasitic capacity in a manner to beopposite to said lead wire sections.
 10. A capacitance-type pressuresensor as defined in claim 9, wherein said parasitic capacity increaserestraining electrode section is formed by projecting a portion of saidcounter electrode in a manner to be entirely opposite to one region onsaid one surface of said base substrate on which said lead wire sectionsare provided.
 11. A capacitance-type pressure sensor as defined in claim6, wherein said sensor is used in a manner to be contacted with fluid ofwhich a pressure is to be measured on a rear surface of said diaphragmsubstrate;said counter electrode being arranged in a manner to extendtoward the outer peripheral portion of said diaphragm substrate so as torestrain an increase in parasitic capacity occurring due to existence ofsaid fluid on said rear surface of said diaphragm substrate, resultingin being opposite to said lead wire sections.
 12. A capacitance-typepressure sensor as defined in claim 11, wherein said counter electrodeis constituted by a disc-like electrode pattern having a diameter, saiddisc-like electrode pattern being disposed opposite to said maincapacitive electrode, said lead wire sections and said referencecapacitive electrode.